Demonstrate the importance of the legal principle of insurable interest in relation to marine cargo of shippers and marine liability of shipowners. Comment why the situation of double insurance does not exist where more than one party have arranged some marine insurance policies for the same consignment of marine cargo e.g., shipowners have P&I insurance, shippers have marine cargo insurance, charterers have charterers' liability insurance, deport operators have insurance of deport operators' liability insurance and truck operators have insurance of truck operators' liability all on the same consignment of marine cargo.